1. Field of the Invention
The present invention relates to a semiconductor structure, and more specifically to a nitride semiconductor structure.
2. Description of Related Art
Nitride light-emitting diode has been widely applied at a variety of fields recently. In the nitride semiconductor structure, since the silicon substrate possesses advantages such as high thermal conductivity and low cost, a large scale nitride semiconductor structure, which uses a silicon substrate as a base, has become an important component of the nitride light-emitting diode.
However, take gallium nitride (GaN) semiconductor layer for example, a difference of a lattice between the gallium nitride semiconductor layer and the silicon substrate is 17%, and a difference of a coefficient of thermal expansion between the both is 54%. The above differences not only cause thin film fracture due to excessive thermal stress during cooling period, but also produce internal stress during the epitaxy process of the gallium nitride semiconductor layer, thereby generate thin film cracks and defect formation. Therefore, an issue desired to be solved is that how to overcome the problem of which the lattice and the coefficient of thermal expansion do not match well between the gallium nitride semiconductor layer and the silicon substrate, so as to reduce epitaxial wafer fracture and avoid defect formation.